Fine root biomass in two black spruce stands in interior Alaska: effects of different permafrost conditions

Key message

In black spruce stands on permafrost, trees and understory plants showed higher biomass allocation especially to ‘thin’ fine roots (diam. < 0.5 mm) when growing on shallower permafrost table.

Abstract

Black spruce (Picea mariana) forests in interior Alaska are located on permafrost and show greater below-ground biomass allocation than non-permafrost forests. However, information on fine roots (roots <2 mm in diameter), which have a key role in nutrient uptake and below-ground carbon flux, is still limited especially for effects of different permafrost conditions. In this study, we examined fine root biomass in two black spruce stands with different depths to the permafrost table. In the shallow permafrost (SP) plot, fine root biomass of black spruce trees was 70 % of that in the deep permafrost (DP) plot. In contrast, ratio of the fine root biomass to above-ground biomass was greater in the SP plot than in the DP plot. Understory plants, on the other hand, showed larger fine root biomass in the SP plot than in the DP plot, whereas their above-ground biomass was similar between the two plots. In addition, biomass proportion of ‘thin’ fine roots (diam. <0.5 mm) in total fine roots was greater in the SP plot than in the DP plot. These results suggest that black spruce trees and understory plants could increase biomass allocation to fine roots for efficient below-ground resource acquisition from colder environments with shallower permafrost table. In the SP plot, fine roots of understory plants accounted for 30 % of the stand fine root biomass, suggesting that understory plants such as Ledum and Vaccinium spp. would have significant contribution to below-ground carbon dynamics in permafrost forests.